I'm a very basic DIYer with little experience and knowledge, I'm new to diesels and dual battery systems, and I don't know much about electrical troubleshooting. Just wanted you to know what you're dealing with before you start reading.

I have a 2015 F350 Lariat CCSB 6.7 with 93,000 miles. Bought used last December. It is bone stock except for a SPE cold side pipe, Titan 60 gallon fuel tank, and aftermarket 5th wheel tailgate. Batteries are Die Hard Gold 850 CCA/150 RA, about two years old, which I inherited from the previous owner.

Yesterday morning was the last day of a 5,000+ mile cross-country trip pulling the 5th wheel. I get in the truck to head home and get a "click, no crank." First time it's ever done that. All the interior lights/bells/whistles seemed to be working normally. It was chilly, but not really cold out, about 30F. Checked battery terminal voltage on both batteries, and it's sitting at 12.31 to 12.32. Not great, especially considering I had just done 7 hours of highway driving the day before. But I thought that should still be enough to turn the engine over, so I'm thinking something other than the batteries. Just for kicks, I asked a fellow camper for a jump, and the truck started right up. Terminal voltage while idling was 14.5, so the alternator seemed to be charging properly. I drove the 4 hours home without shutting the engine off. When I got home, I shut off and restarted several times without incident. I tried doing a poor man's load test by checking voltage while cranking, but was getting erratic readings on the driver's side battery.

This morning, after letting the truck sit in my 50 degree garage overnight, I checked terminal voltage and attempted the load test again. Before attempting to start, I was getting about 12.42 on both batteries, and again I got a "click, no start." Funny thing is, sometimes the driver's side battery will read 0 volts, sometimes it will give a fluctuating voltage, and sometimes it will give a stable 12.xx voltage. Passenger battery always gives a stable 12.xx reading. About an hour later I checked again, and both batteries were reading 12.63 (without ever starting the truck this morning). But sometimes the driver's side battery will read 12.63, and sometimes it will read 0. So at this point I'm thinking that battery has a bad cell or internal short. But before replacing a couple of two year old batteries, I want to be sure there isn't something else going on.

Cables/posts are clean and tight, except for a very small amount of corrosion on the outside of the driver's side negative cable clamp. However, I can see where either the previous owner or the dealer I bought it from cleaned a bunch of corrosion off of both batteries. The corrosion has not re-formed since I bought the truck, other than that very small amount I mentioned. I have not gone chasing the ground connections yet.

I'm not set up for Forscan, but I do have a Veepeek OBDII dongle and the car scanner app. I have two codes showing up, both of which are archived. The first code is c1001(01), which is due to the fact that the backup camera was removed when the aftermarket tailgate was installed. This code has been present since I bought the truck, and probably is not relevant to the no crank. The second code is B1310(14). Car scanner calls it "power door unlock circuit failure," but this site (https://www.dtcdecode.com/Ford) says it's "run/start control circuit short to ground or open."

Relevant to the second code, I've noticed for a while now that I often have to press the unlock button on the key fob a couple of times to get the doors to unlock. One morning I couldn't get it to respond at all and had to unlock with the key. I haven't gotten around to replacing the fob batteries yet, but it happens with both fobs, and the lock button always works on the first press, so I figured the fob batteries weren't the issue. So this seems like a potential obvious connection to the no crank.

So my question at this point is whether an internal battery short is the likely source of the code, the door unlock issue, and the no crank. If so, replace batteries and problem solved. But just want to be sure there isn't something else I should be looking at.

Another newbie question. When I disconnect the batteries, are there any potential negative consequences besides loss of radio presets?

TIA.

Edit: I should add that, despite my newbie status, I do understand that the batteries are wired in parallel, and that any stable 12.xx voltage readings I'm getting with the batteries connected are averaged across the two batteries. I was putting the probes directly on the battery posts, so I'm thinking that the weird stuff I'm seeing with the driver's side voltage readings may indeed be indicative of something going on inside that battery (?).

 

How old are those batteries? That voltage sounds low to me.

 

They are approximately two years old, based on the date sticker on the side. They were in the truck when I bought it. Yes, other than the 12.63 reading I got when I checked later this morning, the voltages do sound low. Especially given that I've been doing almost daily long highway drives for the last month. Also those readings were with everything connected, so probably affected by opening doors and cycling the key. I suppose the proper thing to do would be to take the batteries out and have them load tested without anything connected to them.

 

Try checking voltage on the battery clamp rather than the battery terminals. write it down or remember it
Check voltage direct on the battery terminals. Any difference?
Next check voltage on the clamps but wiggle the clamp wires and see if you notice any voltage fluctuations.

>12.65 is a fully charged battery
You may also have an intermittent short
To test
Remove the negative side of the battery cable
Set your multimeter to amps (Should be 10amp fused)
Make sure the truck computer system is asleep (2015 takes about 10 min after removing key and closing doors)
Make sure the under hood light is not on
Put NEG lead on battery wire clamp
Put POS lead on NEG battery terminal
A reading under 50 milliamps is good, over you either have a parasitic draw which I can explain how to find after you conduct the above

 

Thank you. I'll do that tomorrow morning and report back.

 

Anything under 12.6 V is low. Can you jump it and see if it will turn over?

 

I did successfully jump it the first time it happened. There was a guy at the campground with a diesel Ram who graciously gave me a jump. I haven't tried jumping again at home because our only other vehicle is a 4 cyl Toyota Camry. I'm thinking it might put too much strain on that little alternator. I suppose I ought to buy a jump starter to have on hand for such occasions. Not sure if I can find one locally that's powerful enough for a 6.7 powerstroke.

 

Nah, you won't hurt the alternator with a jump unless you connect the cables wrong.. And with your batteries being that close to charged, it shouldn't take much of a boost.

 

No difference in voltage when checking on clamps vs. directly on terminals.
Clamp wires were tight and didn't wiggle. No change in voltage when I attempted to wiggle.
Amp draw test returned 0.00 on both batteries.
Once I let everything settle down for a while after opening the hood, both batteries read close to fully charged (over 12.6). But still sometimes I'm getting 0.00 volts or weird fluctuating low voltage on the driver's side battery.

I bought a cheap battery tester. Both batteries tested good, although both tested at the lower end of the good range for an 850 CCA battery. I tested with all cables disconnected so nothing going on with the rest of the truck could interfere.

I still get the weird voltage fluctuations on the driver's side battery with both cables disconnected, so whatever is causing it is going on inside the battery. This leads me to believe that battery has an intermittent internal short, despite the good reading from the tester. Sometimes it will read a stable 12.6x volts for a good while, then out of the blue it will start doing the weird fluctuations. This never happens on the passenger side battery, so I don't think the multimeter is acting up.

At this point I'm about ready to replace the batteries, unless there is some other test I can do to shed more light on the situation?

 

This sounds like a simple loose connection......not saying your batteries are good, but typically a bad or loose connection will demonstrate the same symptoms, (power everywhere but won't crank), clean and check every connection from your batteries.

 

If it starts and runs fine otherwise after a jump start, it's obvious to replace the batteries. Could be a dead cell. High engine temps while towing may have cooked them.

I experienced same scenario- click, no start. Voltage measured fine but I didn't bother doing a load test since my batteries were 5 years old. Quick trip to costco for 2 new interstate batteries and back in business. If you do a load test, let them sit overnight and test in the morning for a realistic scenario.

 

I think I've ruled out the batteries as the cause. They both test good and both hold a charge overnight (both above 12.65 after sitting disconnected overnight). The lower readings I was seeing likely were caused by checking too soon after opening doors/hood and cycling the key.

The strange voltage fluctuations I was seeing on the driver's side battery were caused by oxidation on the posts. Although they didn't look corroded, they had a smooth dull gray layer on the outside. After I gave them a vigorous wire brushing to expose bright shiny lead, the voltage fluctuations went away.

Unfortunately the truck still won't crank. So I've got a bad connection, wire, or component somewhere. The B1310(14) code suggests the problem is in the run/start control circuit. I swapped the run/start relay with one of the other identical relays in the fuse box, but no dice. So the relay doesn't appear to be the problem.

I then took the relay out and probed the female pin connections with a test light. One of the larger pins has power to it all the time, as it is supposed to. However, one of the smaller coil pins also has power all the time. I thought it was only supposed to have power when the key is on. But I'm running on bits and pieces of information from youtube and google, so IDK. I'm completely new to wiring diagrams, so I'm having a hard time making sense of the diagrams I'm finding on line. If anyone has any pointers on how to diagnose this circuit, I'm all ears. Otherwise, I'm about ready to throw in the towel and pay someone.

 

Voltage doesn’t start the truck, amps do. That’s why It starts with a jump. Voltage by itself only tells part of the story. You have to check the voltage a second time with a known load applied to get a better picture of battery health. I bet if you'd kept the meter attached while trying to start it you would've seen an absurdly low reading.

Bring the batteries to advance or autozone for load testing. That’s a better path than paying a diagnostic fee or unloading the parts cannon at it.

 

@Wellibe Here is the diagnostic tree for you.


C13 CHECK THE RUN/START RELAY CONTROL CIRCUIT SUPPLY

• Measure the voltage between the run/start relay socket pin 1, circuit SBB45 (GY/RD), harness side and ground.

Is the voltage greater than 10 volts?
Yes GO to C14.
No VERIFY the BJB fuse 45 (10A) is OK. If OK, REPAIR circuit SBB45 (GY/RD). If not OK, REFER to the Wiring Diagrams manual to identify the short to ground in circuit SBB45 (GY/RD). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

C14 CHECK THE RUN/START RELAY CONTROL CIRCUIT GROUND FOR AN OPEN

• Disconnect: BCM C2280F.

• Measure the resistance between run/start relay socket pin 2, circuit CDC55 (BN/VT), harness side and BCM C2280F Pin 18, CDC55 (BN/VT), harness side.

Is the resistance less than 5 ohms?
Yes GO to C15.
No REPAIR circuit CDC55 (BN/VT). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

C15 CHECK THE RUN/START RELAY CONTROL CIRCUIT FOR A SHORT TO GROUND

• Measure the resistance between run/start relay socket pin 2, circuit CDC55 (BN/VT), harness side and ground.

Is the resistance greater than 10,000 ohms?
Yes GO to C16.
No REPAIR circuit CDC55 (BN/VT). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

Yes RECONNECT the electrical connectors and relay. CLEAR the DTCs. REPEAT the self-test. If DTC B1310:14 is still present,
Guided Routine (BCM) only available in the on-line Workshop Manual . No INSTALL a new relay. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

C16 CHECK THE RUN/START RELAY

• Carry out the appropriate relay component test.
  Refer to Wiring Diagrams Cell 149 for component testing.

Is the run/start relay OK?
Yes RECONNECT the electrical connectors and relay. CLEAR the DTCs. REPEAT the self-test. If DTC B1310:14 is still present,
Guided Routine (BCM) only available in the on-line Workshop Manual .
No INSTALL a new relay. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

 

I load tested both batteries using a standard battery tester. Both tested good; voltage didn't drop below the "good" range when the load was applied.